High density, high ductility, high strength tungsten-nickel-iron alloy &amp; process of making therefor

ABSTRACT

A very heavy tungsten alloy for use as armor piercing penetrators and the like, the alloy having high mechanical strength and yet being sufficiently ductile so as not to fracture or fragment upon impact with enemy targets, and preferably comprising about 97.0 weight % tungsten, and 1.5 weight % each of nickel and iron.

United States Patent 1 Sczerzenie et a1.

[ HIGH DENSITY, HIGH DUCTILITY, HIGH STRENGTH TUNGSTEN-NICKEL-IRON ALLOY & PROCESS OF MAKING THEREFOR [75] Inventors: Francis E. Sczerzenie; Frank I.

Zaleski, both of Philadelphia, Pa.

[73] Assignee: Government of the United States as represented by the Secretary of the Army, Washington, DC.

22 Filed: Nov. 10, 1972 211 Appl. No; 305,640

Related US. Application Data [63] Continuation of Ser. No. 111,757, Feb. 1, 1971,

abandoned.

[52] US. Cl. 29/182; 75/176; 75/227; 102/52 [51] Int. Cl 1322f 5/00; F42b 13/04 [58] Field of Search 102/52; 75/176, 214, 221, 75/224, 227; 148/32, 126; 29/182 [56] References Cited UNITED STATES PATENTS 2,793,951 15/1957 Green et al 75/176 X [4 1 June 10, 1975 Primary Examiner-C. Lovell Attorney, Agent, or Firm-Nathan Edelberg; Robert P. Gibson; Arthur M. Suga [5 7 ABSTRACT A very heavy tungsten alloy for use as armor piercing penetrators and the like, the alloy having high mechanical strength and yet being sufficiently ductile so as not to fracture or fragment upon impact with enemy targets, and preferably comprising about 97.0 weight tungsten, and 1.5 weight each of nickel and iron.

2 Claims, N0 Drawings HIGH DENSITY, HIGH DUCTILITY, HIGH STRENGTH TUNGSTEN-NlCKEL-IRON ALLOY & PROCESS OF MAKING THEREFOR The invention described herein may be manufactured, used and licensed by or for the Government for governmental purpose without the payment to us of any royalty thereon.

This is a continuation of application Ser. No. 111,757, filed Feb. 1, 1971, now abandoned.

This invention relates to heavy metal alloys and more particularly concerns alloys of W-Ni-Fe having high strength and high ductility characteristics Preformed penetrators for armor-piercing projectiles and the like for modern day munitions should desirably be of very high density as well as possessing high strength and ductility. Without sufficient ductility, the penetrator may fragment or fracture upon impact with an enemy target. If the target comprises but a single armor layer, fragmenting of the penetrator upon impact therewith might not be unduly detrimental. However, where enemy targets comprise spaced armored layers, as in many modern tanks and flying craft, it is imperative that the penetrator remain integral upon impact if successful penetration of the layers is to be achieved.

Thus, prior art alloy penetrators, if capable of achieving sufficiently high densities were either brittle and/or of low strength, or, if sufficiently strong and ductile, did not possess a critical density of at least about 18.5 g/cc.

It is therefore an object of this invention to provide a heavy metal alloy having a nominal density of at least about 18.5 g/cc.

Another object is to provide such an alloy having high strength and high ductility properties, thus making it suitable for preformed penetrators for warhead application.

The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the specification that follows.

In accordance with the above objects, we have discovered that a W base alloy which includes minor proportions of Ni and Fe, will yield a highly ductile and strong alloy having a high density.

More specifically, we have found that when about 97.0 weight of W is formed into an alloy containing Ni and Fe in about a l to 1 proportion through our powder metallurgical processes that an alloy having a nominal density of about 18.5 g/cc is achieved while yielding an average elongation in 1 inch of about 1 1%, an ultimate tensile strength averaging 137 ksi. and a yield strength (0.2% offset) of about 100 ksi.

In producing our inventive alloy, we blend fine, high purity tungsten, nickel and iron powders in a suitable apparatus, such as a Twin Shell blender, for example. The powders are at least about 99.9% pure and should pass through a 325 mesh screen, and preferably be of to 40 microns diameter. The blend is conditioned for compaction by a suitable synthetic atomized paraffin wax, preferably 2 to 5 microns in diameter. The wax functions as a die lubricant and to impart green strength to the molded piece. Table I below lists the weight percentages and effective ranges of our alloy compositions.

TABLE I 18.5 g/cc W-Ni-Fe Heavy Alloy The range of tungsten is critical in the above formulations. If the percentage tungsten is reduced below about weight the required nominal density of about 18.5 g/cc will not be achieved. If the tungsten percentage approaches about 98 weight the resultant matrix of Ni and Fe is weak and a high density alloy cannot be achieved.

The ratio of Ni to Fe is preferably 1 to 1, although we have found that ratios of about 40-60 to 60-40 are satisfactory.

The blended powdered metals with synthetic wax are then placed in a die and pressed to a green density compact of at least 1 1.6 g/cc. Any green density lower than about this value produces a sintered piece having a nominal density below 18.5 g/cc.

The pressed compact will now be placed in a furnace at about 540C under a dry (at least 40F dew point) reducing atmosphere (hydrogen or dissociated ammonia) and heated in a period of about 30 minutes to about 875C and maintained at this temperature for about another 30 minutes. The compact will then be rapidly transferred to another furnace also containing a dry reducing atmosphere, but which is maintained at a temperature ranging between about l,460 to 1,600C. At the higher temperature of 1,600C, greater densification results. However, above about 1,600C, the compact bloats and blisters. The compact is held at this temperature for about 1 to 2 hours for densification by liquid phase sintering. The matrix of Ni and Fe liquifies and very considerable shrinkage of the compact occurs after densification has taken place. No traces of the wax remains after this sintering operation. The piece may now be slow cooled and quenched to yield optimum mechanical properties. From a sintering temperature of about 1,600C, it is slow cooled to about 1,300-1,400C in a period of time which is dictated by the mass of the compact or piece. As a general rule, a cooling rate of about 15C/minute for each 40g of mass has been found quite satisfactory. One skilled in this art will know at approximately what rate pieces of varying sizes and masses should be cooled in order that voids will not be present in the piece and to insure total homogeneity in the matrix phase.

After the piece has been sufficiently slow cooled, it is quenched in a water-jacketed cooling chamber having a controlled atmosphere therein of hydrogen or dissociated ammonia.

Further uses for our inventive alloy reside in its effectiveness as an X-ray shield, even more effective than the currently used lead shielding. Our alloy may also be used advantageously in various other applications wherever an extremely high density material is needed.

We wish it to be understood that we do not desire to be limited to the exact details described, for obvious modifications will occur to a person skilled in the art.

We claim:

1. A preformed penetrator for armor-piercing projectiles comprising an as-sintered alloy having at room temperature, a nominal dendity of 18.5 g/cc, a yield strength (.2% offset) of 100 ksi, an ultimate tensile strength of 137 ksi, an elongation in 1 inch of 1 1%, said alloy produced by the steps of blending fine powders of tungsten, nickel and iron with a minor proportion of an atomized synthetic wax to form a blended mix,

pressing said blended mix to a density of at least 1 1.6

g/cc to form a green compact,

sintering said green compact for densification thereof, and

cooling said densified sintered piece to form a finished piece devoid of voids and a matrix phase of nickel and iron totally homogeneous, said cooling being further characterized by the steps of slow-cooling said sintered piece to a temperature of about 1,300l,400C at a rate of about 15C/minute, and

quenching said slow-cooled piece to below about room temperature in a reducing atmosphere chamber, said alloy consisting of, by weight,

about 97% tungsten,

about 1.5% nickel, and

about 1.5% iron.

2. A process for fabricating an as-sintered heavy tungsten alloy preformed penetrator for use in armor piercing projectiles consisting of, by weight,

about 97% tungsten, about 1.5% nickel, and about 1.5% iron 5 and comprising the steps of blending fine powders of tungsten, nickel and iron with a minor proportion of an atomized synthetic wax to form a blended mix,

pressing said blended mix to a density of at least 1 1.6

g/cc to form a green compact,

sintering said green compact for densification thereof,

and cooling said densified sintered piece to form a finished piece devoid of voids and a matrix phase of nickel and iron totally homogeneous, said finished piece having at room temperature, a nominal density of at least about 18.5 g/cc, a yield strength (.2% offset) of lOOksi, an ultimate tensile strength of 137 ksi, and an elongation in 1 inch of l 1%, said cooling being further characterized by the steps of slow-cooling said sintered piece to a temperature of about 1,3001400C at a rate of about 15C/minute, and

quenching said slow-cooled piece to below about room temperature in a reducing atmosphere cham- 

1. A PREFORMED PENETRATOR FOR ARMOR-PIERCING PROJECTILES COMPRISING AN AS-SINTERED ALLOY HAVING AT ROOM TEMPERATURE, A NOMINAL DENDITY OF 18.5 G/CC, A YIELD STRENGTH (.2% OFFSET) OF 100 KSI. AN ULTIMATE TENSILE STRENGTH OF 137 KSI, AN ELONGATION IN 1 INCH OF 11%, SAID ALLOY PRODUCED BY THE STEPS OF BLENDING FINE POWDERS OF TUNGSTEN, NICKEL AND IRON WITH A MINOR PROPORTION OF AN ATOMIZED SYNTHETIC WAX TO FORM A BLENDED MIX, PRESSING SAID BLENDED MIX TO A DENSITY OF AT LEAST 11.6 G/CC TO FORM A GREEN COMPACT, SINTERING SAID GREEN COMPACT FOR DENSIFICATION THEREOF, AND COOLING SAID DENSIFIED SINTERED PIECE TO FORM A FINISHED PIECE DEVOID OF VOIDS AND A MATRIX PHASE OF NICKEL AND IRON TOTALLY HOMOGENEOUS, SAID COOLING BEING FURTHER CHARACTERIZED BY THE STEPS OF SLOW-COOLING SAID SINTERED PIECE TO A TEMPERATURE OF ABOUT 1,300*-1,400*C AT A RATE OF ABOUT 15*C/MINUTE, AND QUENCHING SAID SLOW-COOLING PIECE TO BELOW ABOUT ROOM TEMPERATURE IN A REDUCING ATMOSPHERE CHAMBER, SAID ALLOY CONSISTING OF, BY WEIGHT, ABOUT 97% TUNGSTEN, ABOUT 1.5% NICKEL, AND ABOUT 1.5% IRON.
 2. A process for fabricating an as-sintered heavy tungsten alloy preformed penetrator for use in armor piercing projectiles consisting of, by weight, about 97% tungsten, about 1.5% nickel, and about 1.5% iron and comprising the steps of blending fine powders of tungsten, nickel and iron with a minor proportion of an atomized synthetic wax to form a blended mix, pressing said blended mix to a density of at least 11.6 g/cc to form a green compact, sintering said green compact for densification thereof, and cooling said densified sintered piece to form a finished piece devoid of voids and a matrix phase of nickel and iron totally homogeneous, said finished piece having at room temperature, a nominal density of at least about 18.5 g/cc, a yield strength (.2% offset) of 100ksi, an ultimate tensile strength of 137 ksi, and an elongation in 1 inch of 11%, said cooling being further characterized by the steps of slow-cooling said sintered piece to a temperature of about 1, 300* -1400*C at a rate of about 15*C/minute, and quenching said slow-cooled piece to below about room temperature in a reducing atmosphere chamber. 